1. Field of Invention
The present invention relates to a resistive random access memory (RRAM) and, in particular, to an RRAM having the characteristics of a diode and a resistive memory.
2. Related Art
Non-volatile memories have been widely used in many portable electronic devices such as cell phones, digital cameras, PDAs, notebook computers since they does not need continuous power to maintain the writing states and have lower power consumption. In various kinds of non-volatile memories, the flash RAM having the properties of fast writing and fast erasing is one of the most popular products. However, since the smaller size cells are developed, the flash RAM definitely encounters the challenges of large writing voltage, long writing time, and short registering time due to the thinner gate. Accordingly, it is desired to develop new non-volatile memories to substitute the flash RAM. Among the new non-volatile memories, the RRAM has drawn the researcher's attentions since it has the advantages of short writing and erasing time, low operation voltage and current, long retention time, multiple state storage, simple structure, simple writing and reading process, and small cell size. In other words, the RRAM is the most potential technique and is the critical research in non-volatile memories.
When the RRAM is applied to the 3D high-density crossbar structure memory cell array, the interference between the elements may occur. Thus, a selective element, such as a transistor or a diode, is needed to connect with the RRAM. In the present researches, a diode is a preferred selective element for the RRAM. Since the diode is made of oxide, which can be formed without high-temperature processes and has good rectification property, it can used as a perfect selective element. Therefore, the one diode-one resistor (1D1R) device is considered as a simplest memory cell and it is the most potential structure for developing non-volatile memories.
However, a general PN junction diode is composed of a P-type oxide and an N-type oxide, and it is not easy to control the compositions of these two oxide layers. In addition, the problem of unstable operation voltage and resistance states of RRAM may easily generate errors in operation.
Therefore, it is an important subject to provide a RRAM that can overcome the above problems and provide the excellent performance.